1. Field of the Invention
The present invention relates to a method of manufacturing a capacitor, and more particularly to a method of manufacturing a capacitor comprising a capacitor dielectric film made of an oxide.
2. Description of the Background Art
FIGS. 13 to 17 are sectional views sequentially showing the steps of a method of manufacturing a semiconductor device comprising a capacitor according to the prior art. First of all, an element isolating film 102 is formed on an upper face of a semiconductor substrate 101. Then, a gate structure having a gate oxide film 104 and a gate electrode 105 provided in that order is selectively formed on the upper face of the semiconductor substrate 101 in an element forming region. Next, ions are implanted by using the gate structure and the element isolating film 102 as masks. Consequently, a source region 103s and a drain region 103d are formed in the upper face of the semiconductor substrate 101 (FIG. 13).
Subsequently, an insulating film 106 covering side and upper faces of the gate structure is formed, and a bit line 107 is then formed in contact with the source region 103s. Thereafter, an insulating film is deposited over the whole face and is then etched back. Consequently, an interlayer insulating film 109 is formed. Next, a contact hole 110 reaching an upper face of the drain region 103d from an upper face of the interlayer insulating film 109 is formed and a plug layer 111 to fill in the contact hole 110 is then formed (FIG. 14).
Next, a barrier metal layer is formed over the whole face. Then, a noble metal film is formed on the barrier metal layer by a sputtering method or a CVD method using an organic noble metal compound for a source. Then, a resist having a predetermined opening pattern is formed on the noble metal film. By using the resist as a mask, thereafter, the noble metal film and the barrier metal layer are subjected to etching in that order by an anisotropic dry etching method in a gas plasma atmosphere. Consequently, a barrier metal layer 112 to come in contact with the plug layer 111 and a storage node 113 are formed (FIG. 15).
Subsequently, a noble metal film is formed over the whole face by the sputtering method or the CVD method using an organic noble metal compound for a source. Then, the noble metal film is subjected to etching by the anisotropic dry etching method in the gas plasma atmosphere. Consequently, a side wall portion 114 is formed on side faces of the barrier metal layer 112 and the storage node 113 (FIG. 16). The side wall portion 114 functions as a first electrode of a capacitor together with the storage node 113.
Next, a capacitor dielectric film 115 made of a high dielectric film or a ferroelectric film is formed over the whole face. Subsequently, a cell plate 116 functioning as a second electrode of the capacitor is formed on the capacitor dielectric film 115. Then, an insulating film is formed on the cell plate 116, and is thereafter etched back, thereby forming an interlayer insulating film 117. Next, an aluminum wiring 118, an interlayer insulating film 119, an aluminum wiring 120 and a protective film 121 are formed in that order by a well-known method. Thus, a device is completed (FIG. 17).
However, such a method of manufacturing a semiconductor device according to the prior art has had the following problems.
First Problem
According to the method of manufacturing a semiconductor device according to the prior art, a noble metal film is processed by the anisotropic dry etching method at the steps shown in FIGS. 15 and 16. However, a noble metal generally has a very poor workability. For example, at the step of etching the noble metal film shown in FIG. 15, a reaction product generated by the etching is deposited on the side face of the storage node 113 or the like to form a re-deposited film so that the side face of the storage node 113 becomes tapered in some cases. A foreign matter removing method of removing the re-deposited film has also been known. However, a material of the re-deposited film is almost the same as that of the storage node 113 and depositing force for the storage node 113 is comparatively great. Therefore, removing force for removing the re-deposited film should be set great. For this reason, if a size of the storage node 113 is reduced with microfabrication of a semiconductor device, the storage node 113 itself is also removed at the foreign matter removing step. Accordingly, there has been a problem in that it is very difficult to form a fine storage node 113 having a half pitch of 0.25 xcexcm or less (The half pitch means half of a formation pitch of a structure which is formed repetitively at regular intervals. In FIG. 15, for example, the half pitch is equivalent to half of a space between a left end of the storage node 113 on the left side and a left end of the storage node 113 on the right side).
Second Problem
As described with reference to the steps shown in FIGS. 15 and 16, the noble metal film can be formed by the sputtering method or the CVD method. In consideration of the goodness of step coverage, however, it is desirable that the noble metal film should be formed by the CVD method. An example of a method of forming a storage node using the step of depositing a noble metal film by the CVD method has been disclosed in Japanese Laid-Open Patent Publication No. Hei 10-289985. In the case where the noble metal film is to be formed by the CVD method, an organic noble metal compound has conventionally been used as a source of the CVD.
However, if the organic noble metal compound is used as the source of the CVD, carbon or an organic molecule which is contained in the source of the CVD remains in the storage node 113 and the side wall potion 114. There has been a problem in that the remaining carbon or organic molecule causes an oxidation reaction when the capacitor dielectric film 115 is deposited at the next step, thereby generating carbon dioxide and water.
Under the present circumstances, all the high dielectric films or ferroelectric films which are the materials of the capacitor dielectric film 115 are oxides. Accordingly, when the capacitor dielectric film 115 is to be formed, it is essential that the atmosphere should be set to have oxidation properties. Therefore, it is impossible to prevent the carbon dioxide and water from being generated by the carbon or organic molecule remaining in the storage node 113 and the side wall portion 114. In addition, the noble metal generally has a high catalytic action for an oxidation-reduction reaction. For this reason, the oxidation reaction is caused more easily.
The carbon dioxide and the water which are generated by the oxidation reaction affect a semiconductor device in the following manner. Referring to a bad influence of the carbon dioxide, first of all, the carbon dioxide is an acidic gas and easily reacts to a high dielectric film or a ferroelectric film which is a basic oxide, thereby generating a carbonate. For example, in the case where barium strontium titanate ((Ba, Sr) TiO3: BST) is used as the high dielectric film, an acid-base reaction represented by the following reaction formula is easily caused.
(Ba, Sr)TiO3+CO2xe2x86x92(BaCO3+SrCO3)+TiO2 
(A reaction factor is omitted.)
As a result, a carbonate of an alkaline earth metal is generated in the high dielectric film or the ferroelectric film. The carbonate causes a decrease in a dielectric constant and a deterioration in a breakdown voltage and reliability.
Referring to a bad influence of the water, when the generated water is decomposed on a surface of the storage node 113 to generate hydrogen, the hydrogen reduces the high dielectric film or the ferroelectric film, resulting in a deterioration in a breakdown voltage. Furthermore, if the carbonate is generated as described above, the water dissolves the carbonate. Therefore, the water has a seriously bad influence such as peeling of a film as well as the deterioration in a breakdown voltage and reliability.
A first aspect of the present invention is directed to a method of manufacturing a capacitor, comprising the steps of (a) processing a predetermined film made of a material having a more excellent workability than a noble metal film to form a structure in a region in which a first electrode of a capacitor is to be formed on a main surface of an underlying layer, (b) substituting a noble metal element for a predetermined element contained in the structure, thereby forming the first electrode, (c) forming a capacitor dielectric film made of an oxide on the first electrode after the step (b), and (d) forming a second electrode of the capacitor on the capacitor dielectric film.
A second aspect of the present invention is directed to the method of manufacturing a capacitor according to the first aspect of the present invention, wherein the step (b) is executed by exposing the first electrode into a noble metal halide atmosphere while heating the first electrode.
A third aspect of the present invention is directed to the method of manufacturing a capacitor according to the second aspect of the present invention, wherein the noble metal halide is an inorganic noble metal halide.
A fourth aspect of the present invention is directed to the method of manufacturing a capacitor according to the second aspect of the present invention, wherein, at the step (b), the noble metal halide is generated by causing a noble metal element and a halogen gas to react to each other in a reaction chamber in which the capacitor is put.
A fifth aspect of the present invention is directed to a method of manufacturing a capacitor, comprising the steps of (a) forming a first electrode of a capacitor on a main surface of an underlying layer by utilizing a CVD method using an inorganic noble metal halide for a source, (b) forming a capacitor dielectric film made of an oxide on the first electrode, and (c) forming a second electrode of the capacitor on the capacitor dielectric film.
A sixth aspect of the present invention is directed to the method of manufacturing a capacitor according to the fifth aspect of the present invention, wherein, at the step (a), the inorganic noble metal halide is generated by causing an inorganic noble metal element and a halogen gas to react to each other in a reaction chamber in which the capacitor is put.
According to the first aspect of the present invention, the first electrode made of the noble metal element can be formed without executing the step of processing a noble metal film having a poor workability. Moreover, the first electrode has the same three-dimensional configuration as the structure. Therefore, the first electrode which is fine can also be formed by finely processing a predetermined film having an excellent workability.
According to the second aspect of the present invention, the noble metal halide has very great oxidizing force. Therefore, the noble metal halide can easily react to the predetermined element contained in the structure to precipitate a noble metal, and can evaporate the predetermined element contained in the structure as a halide having a high vapor pressure from the structure.
According to the third aspect of the present invention, it is possible to avoid the execution of the step of depositing a noble metal film by the CVD method using an organic noble metal compound for a source. Therefore, it is possible to solve various problems of the conventional method of manufacturing a capacitor which are caused by the generation of a carbonate and water.
According to the fourth aspect of the present invention, the noble metal halide used as the raw material is not directly introduced into the reaction chamber but a noble metal element and a halogen gas which are more inexpensive and can be handled more easily than the noble metal halide are used as raw materials and are caused to react to each other in the reaction chamber. Consequently, a noble metal halide is generated. Accordingly, it is possible to avoid the use, as a raw material, of the noble metal halide which is expensive and is to be handled with care. Thus, it is possible to obtain a reduction in a cost and the like.
According to the fifth aspect of the present invention, it is possible to avoid the execution of the step of depositing a noble metal film by a CVD method using an organic noble metal compound for a source. Therefore, it is possible to solve various problems of the conventional method of manufacturing a capacitor which are caused by the generation of a carbonate and water.
According to the sixth aspect of the present invention, the inorganic noble metal halide used as the raw material is not directly introduced into the reaction chamber but an inorganic noble metal element and a halogen gas which are more inexpensive and can be handled more easily than the inorganic noble metal halide are used as raw materials and are caused to react to each other in the reaction chamber. Thus, an inorganic noble metal halide is generated. Accordingly, it is possible to avoid the use, as a raw material, of the inorganic noble metal halide which is expensive and is to be handled with care. Thus, it is possible to obtain a reduction in a cost and the like.
In order to solve the above-mentioned problems, it is an object of the present invention to provide a method of manufacturing a semiconductor device comprising a capacitor having a capacitor dielectric film made of an oxide in which it is possible to form a fine storage node made of a noble metal and to avoid the execution of the step of depositing a noble metal film by a CVD method using an organic noble metal compound for a source.
These and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.